Stage 7 polish: app shell + nav + lobby + settings (Parts A/B/C)

- Screen.svelte shell: nav bar grows, ad+content+tabbar pinned bottom (mobile feel)
- AdBanner.svelte + banner.ts rotator (params, mock long/short, linkify); Header CSS chevron + grow; Menu (bigger CSS hamburger); TabBar + HoldConfirm shared components; user-select:none
- Lobby: hide-empty sections, tab order New/Tournaments/Stats, place-based result badges (result.ts)
- Settings: Board style > Labels (beginner/classic/none) + prefs plumbing (boardlabels.ts); i18n keys + ru mirror

ui/src/lib/boardlabels.ts

@@ -0,0 +1,36 @@
+// Bonus-square label modes (a client setting, separate from the theme). The board
+// renders these locally — premiums are not on the wire. Default is "beginner".
+
+import type { Premium } from './premiums';
+import type { Locale } from './i18n/catalog';
+
+export type BoardLabelMode = 'beginner' | 'classic' | 'none';
+
+export type BonusLabel =
+  | { kind: 'single'; text: string }
+  | { kind: 'split'; top: string; bottom: string }
+  | null;
+
+function multiplier(p: Premium): number {
+  return p === 'TW' || p === 'TL' ? 3 : 2;
+}
+
+function isWord(p: Premium): boolean {
+  return p === 'TW' || p === 'DW';
+}
+
+/**
+ * bonusLabel returns how a premium square is labelled: `classic` "3W"/"3С", `beginner`
+ * a split "3×" / "word" (localized), or nothing.
+ */
+export function bonusLabel(mode: BoardLabelMode, p: Premium, locale: Locale): BonusLabel {
+  if (mode === 'none' || p === '') return null;
+  const n = multiplier(p);
+  const word = isWord(p);
+  if (mode === 'classic') {
+    const tag = locale === 'ru' ? (word ? 'С' : 'Б') : word ? 'W' : 'L';
+    return { kind: 'single', text: `${n}${tag}` };
+  }
+  const bottom = locale === 'ru' ? (word ? 'слово' : 'буква') : word ? 'word' : 'letter';
+  return { kind: 'split', top: `${n}×`, bottom };
+}